Proteoglycan-induced arthritis (PGIA) is a polygenic to immune urine model for rheumatoid arthritis (RA). In this model, genetically susceptible BALB/c females develop arthritis earlier on than the BALB/c males. Genome-wide scans of F2 crosses between the arthritis-susceptible BALB/c strain and several arthritis-resistant murine strains indicated that sex is a major moderator of clinical traits of the disease, and influences B- and T-cell responses. We have found that QTLs which control severity, susceptibility and onset of PGIA, were significantly sex-biased. Linkage analysis identified 2 loci on chromosome 15: Pgia8 locus controls PGIA severity in females, and Pgia9 locus is responsible for the arthritis severity in males only. Using marker-assisted breeding, we transferred the entire chromosome 15 and chromosome Y of DBA/2 into BALB/c genetic background and generated a double consomic strain: BALB/c- 15DBA/2yDBA/2 (B.^DYD). Female B-15D mice were significantly less PGIA-susceptible than BALB/c females, while double consomic B-15 DYD males developed PGIA even earlier than the most susceptible wild type BALB/c females. This proposal hypothesizes that chromosomes 15 and Y both have strong but opposite and significantly sex-biased effects upon susceptibility and severity in the PGIA animal model. We propose to investigate separate and mutual effects of chromosomes 15 and Y on clinical and immunological phenotypes of PGIA through the generation of several congenic strains, which carry either chromosome 15 or hromosome Y loci in arthritis-susceptible BALB/c background. This strategy will facilitate the discovery of the arthritis genes located on these 2 chromosomes and provide insight into the mechanisms of sex-restricted gene function. [unreadable] [unreadable] [unreadable]